1. Field of the Invention
The present invention relates to a light-illuminating probe used for observing a specific cell, a diseased cell, a tumor, or a diseased part, and to a fundus observing apparatus, a fundus surgery apparatus, an endoscope, and a catheter using the light-illuminating probe.
2. Related Art
A fluorescence diagnosis method is well known as a diagnosis method for a cancer or a pathological lesion tissue in a medical field. The fluorescence diagnosis method is a method of detecting a specific cell or a diseased cell by marking the specific cell or the diseased cell with a fluorescent agent, illuminating the cell with an external light corresponding to absorption spectrum, and detecting fluorescent light emitted from the fluorescent agent.
In order to improve detection performance in the diagnosis method, it is necessary to increase an intensity of the external light (hereinafter, referred to as an external illuminating light or an illuminating light) that illuminates the fluorescent agent. Due to the increase in the intensity of the illuminating light, the marked specific cell or diseased cell can be easily detected with the strong fluorescent light emitted from the fluorescent agent.
A light illuminating surgical method that is called “photo-assist” is well known as a surgical method using the external illuminating light. In this surgical method, nano-shell particles having photo-absorption property are injected into a tumor or a diseased cell, and an external light is illuminated, so that the tumor or the like necrotizes or is thermally destructed by photothermal conversion of the nano-shell particles. In addition, a pharmacological therapy (photoreactive agent excitation method) is also well known as that treating a localized diseased part by using a photoreactive agent technique.
In these surgical methods, in order to accelerate necrosis or improve thermal destruction effect and an efficiency of generating a photo-induced reactive agent, it is necessary to increase the intensity of the external illuminating light. In order to increase the intensity of the external illuminating light, the following two requirements are considered.
As the first requirement, when a light illuminating apparatus illuminates a target object such as a specific cell, a diseased cell, a tumor, or a diseased part with an external illuminating light in close proximity thereto, the light illuminating apparatus must not obstruct a field of view for monitoring and observing the illuminated objective area by the separately-disposed monitoring/observing device. As the second requirement, an illuminated spatial range of the external illuminating light must be suitably set in order not to obstruct the field of view for monitoring and observing.
The first requirement is provided due to the following reason, such that, when the external illuminating light propagates through a body fluid or a Ringer's solution onto the diseased part, the light is scattered by micro granules in the body fluid or the Ringer's solution along the optical path of the light. The scattered light leads to flare, so that the target object cannot be easily detected, monitored, or observed by the monitoring/observing apparatus.
The second requirement is provided due to the following reason, such that, if the illuminated spatial range of the external illuminating light is narrow, only the actually-illuminated cells among the cells marked with the fluorescent agent can emit fluorescent light. Therefore, the object that all the marked specific cells, diseased cells, tumors, diseased parts are to be detected cannot be always detected.
In order to solve the problems, there is a method for illuminating the specific cells, diseased cells, tumors, or diseased parts by using an optical fiber provided for the purpose of the light illuminating apparatus in close proximity to the specific cells or the like. According to the method, although the light is illuminated in front of the optical monitoring/observing apparatus, the optical fiber does not obstruct the field of view since the optical fiber has a small size. In addition, since the optical fiber illuminates the target object in close proximity thereto, light scattering caused by the medium between the optical fiber and the target object can be reduced. Accordingly, the first requirement that the light illuminating apparatus in close proximity to the target object must not obstruct the field of view for monitoring and observing is satisfied.
In an inner portion of a core of the optical fiber explained above as provided for the purpose of the light illuminating apparatus, a wave front of the propagating light is maintained to be a flat plane which is perpendicular to an axis of the propagating light, but in an outside of the optical fiber, the wave front is not maintained to be the flat plane due to spread of the light propagating in a free space. The spread angle in the optical fiber is at most 5 degrees, and the illuminated spatial range of the illuminating light from the end portion of the optical fiber is narrow, that is, several degrees. Therefore, the field of view for monitoring and observing is narrowed. However, if the end portion of the optical fiber is moved backwards from the monitoring/observing apparatus so as to spread the illuminating light, scattering occurs, or some portion of the illuminating light is blocked by the monitoring/observing apparatus. Therefore, the field of view for monitoring and observing is obstructed. In order to solve the problems, it is necessary to increase spatial spread of the external illuminating light from the end surface of the optical fiber.
Conventionally, there has been contrived an end-portion structure for increasing the spatial spread of the external illuminating light by forming the end portion of the optical fiber in a parabolic shape such as a shape of bullet (for example, see Patent Document 1).
[Patent Document 1] Japanese Patent Application Publication No. 2003-111789 (P. 6-7, FIG. 2)
FIG. 50(a) is a cross-sectional view illustrating a part of a conventional light-illuminating probe 100 for which the optical fiber 102 has the aforementioned end-portion structure. FIG. 50(b) is a front view of the end portion corresponding to FIG. 50(a) regarding the conventional light-illuminating probe. Since the end portion of the light-illuminating probe 100 has a shape of a bullet in the end portion 101 of the optical fiber 102, the external illuminating light emitted from the end portion 101 of the optical fiber 102 is scattered so that the light can be illuminated with a wide spatial range.
Since the external illuminating light emitted from the end portion 101 of the optical fiber 102 spatially spreads, the illuminating light can be used for a photodynamic therapy (PDT). This is because uniform illumination in the peripheral directions of the optical fiber 102 can be obtained.
As another application, the external illuminating light of the optical fiber 102 can be used for dissolving the plaque or thrombus that causes blood vessel or artery to be narrowed, by using a photoactive agent and performing uniform illumination.
The shape of the end portion 101 of the optical fiber 102 is not limited to a specific one, but any parabolic shape of the longitudinal cross section of the end portion of a optical fiber 102 may be used.
In addition to the core/clad structure that is based on a difference between refractive indexes thereof or a difference caused by refractive index distribution, a light-guiding fiber constructed with a transparent dielectric material and a metal layer surrounding the transparent dielectric material or a hollow optical fiber including a plurality of hollow cylinders in a transparent dielectric material may be used as the optical fiber. Except for a case where a type of the optical fiber is specified, the aforementioned optical fibers are collectively referred to as an optical fiber for the simplification of description.
However, as shown in FIG. 51, the enlargement of the illuminated spatial range of the external illuminating light by using only the scattering at the end portion 101 of the optical fiber 102 also leads to back scattering light 103. Due to the back scattering light 103, the micro granules in the body fluid or the Ringer's solution located behind the end portion of the optical fiber 102 collide with the back scattered light, so that flare occurs in the field of view of the monitoring/observing apparatus located behind the end portion 101 of the optical fiber 102. Therefore, an image having the so-called poor “clearness” is obtained in the field of view, so that the fluorescent light cannot be easily detected.
In addition, the expansion of the illuminated spatial range of the external illuminating light by using only the scattering at the end portion 101 of optical fiber 102 leads to a decrease in intensity of the light that is to be induced to the distal end portion of the probe among the light induced through a light-transmitting portion due to the back scattering light 103. Therefore, there is a need for increasing the intensity of light that is induced to the optical fiber 102.
In addition, since the end portion 101 of the optical fiber 102 is subject to a rounding process, the light-illuminating probe 100 illustrated in FIG. 50(a) has a problem such that the wave front of the propagating light at the end portion 101 of the optical fiber 102 is curved. After emission to the free space, the propagating light is undesirably condensed due to the condensing function of the rounding-processed portion. Therefore, a desired spatial spread cannot be obtained.